Defining melanoma combination therapies that provide senolytic sensitivity in human melanoma cells

Malignant Melanoma that resists immunotherapy remains the deadliest form of skin cancer owing to poor clinically lasting responses. Alternative like genotoxic or targeted chemotherapy trigger various cancer cell fates after treatment including cell death and senescence. Senescent cells can be eliminated using senolytic drugs and we hypothesize that the targeted elimination of therapy-induced senescent melanoma cells could complement both conventional and immunotherapies. We utilized a panel of cells representing diverse mutational background relevant to melanoma and found that they developed distinct senescence phenotypes in response to treatment. A genotoxic combination therapy of carboplatin-paclitaxel or irradiation triggered a mixed response of cell death and senescence, irrespective of BRAF mutation profiles. DNA damage-induced senescent cells exhibited morphological changes, residual DNA damage, and increased senescence-associated secretory phenotype (SASP). In contrast, dual targeted inhibition of Braf and Mek triggered a partially reversible senescence-like state without DNA damage or SASP. To assess the sensitivity to senolytics we employed a novel real-time imaging-based death assay and observed that Bcl-xl/Bcl-2 inhibitors and piperlongumine were effective in promoting death of carboplatin-paclitaxel and irradiation-induced senescent melanoma cells, while senescent-like cells resulting from Braf-Mek inhibition remained unresponsive. Interestingly, a direct synergy between Bcl-2/Bcl-xl inhibitors and Braf-Mek inhibitors was observed when used out the context of senescence. Overall, we highlight that the hallmarks of melanoma senescence and sensitivity to senolytics are context dependent and provide evidence of effective combinations of senotherapy drugs that could reduce treatment resistance while also discussing the limitations of this strategy in human melanoma cells.